1. Field of the Invention
This invention is related to the field of processors and computer systems, and more particularly to the use of known good code in such systems to enable processor architecture extensions, control on-board devices, and other uses.
2. Description of the Related Art
Processors are designed to execute instructions defined in an instruction set architecture (ISA). The ISA defines the instructions, how they are encoded, and what operations occur when they are executed. The ISA generally also defines the various modes of operation of the processor, and other information that a programmer may require in order to successfully code a program for the processor to accomplish the desired operation. In other words, the ISA is essentially a description of how the processor operates when provided with an instruction stream to execute.
Because the programmer relies on the processor to operate as specified in the ISA, modifications to the ISA must be made carefully, and typically with significant input from both programmers (or software companies) and the processor designers (or processor manufacturers). The processor must implement the ISA modifications in hardware to ensure that the required behavior is provided by the processor. Thus, the definition of the changes must be carefully described and agreed upon since a new hardware generation of the processor will be needed to implement the changes. Subsequent modifications would require still further hardware generations.